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Photon generation

  1. Dec 2, 2008 #1
    is the only way to generate a photon by knocking an electron into a higher energy level and when it jumps back to its original energy level it releases the photon because of its excess energy. and wouldnt that mean that an electrical current is always needed so that the electron can initially be knocked into that higher energy level.
     
  2. jcsd
  3. Dec 3, 2008 #2
    Photons are generated when a charged particle undergoes acceleration, during a molecular, atomic or nuclear transition to a lower energy level, during fusion and fission reactions, and when a particle and its antiparticle are annihilated.
     
  4. Dec 3, 2008 #3

    ZapperZ

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    The light that comes from your incandescent light bulbs is not from electrons making an atomic transition. And neither is the light generated at all those synchrotron light sources around the world. And we haven't even touched upon gamma ray sources.

    Zz.
     
  5. Dec 3, 2008 #4
    So, where do photons come from?
     
  6. Dec 3, 2008 #5

    malawi_glenn

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    They are "created", from the vacuum.

    Also it depends on what formalism you are using.
     
  7. Dec 3, 2008 #6
    No formalism other than ordinary English.

    The vacuum thing is interesting, though. I'm not sure what to make of it. Are you saying that something can come from nothing? This seems to violate all kinds of conservation laws!
     
  8. Dec 3, 2008 #7

    malawi_glenn

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    i) English is not any subdiscipline of physics...

    I meant it matters if you have a classical electrodynamics approach or a Quantum Electrodynamical approach to it..

    ii) The Vacuum is not "empty" in physics.

    iii) How you think universie began to exist? ;)

    What is interesting is conservation of momentum, energy and electric charge here.
     
  9. Dec 3, 2008 #8
    I sure see a lot of English words in this forum.

    Which approach should I have? I'm assuming QED since its more recent. Let's stick with that one. (I just hope it can be translated into English!)

    Vacuum seems a rather poor choice of words then. I always hear about the "field". Perhaps that is a good choice of words for "spacestuff"?

    Let's not go down that road just yet!
     
  10. Dec 3, 2008 #9

    malawi_glenn

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    propagator, path integral, wick rotation, are english words, but what do they mean? ;-)

    Should have? ok, the photon is created from the vacuum.


    This is physics, we DEFINE vacuum and annihilation from OUR prescription! Even thoug they can sound phiolosophical incoherent and non logic. So don't come here and tell us how we should name our definitions, theorems etc.
     
  11. Dec 3, 2008 #10
    What is the physics definition for "vacuum"?
     
  12. Dec 3, 2008 #11

    malawi_glenn

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    Just to confuse you even more, it can mean many things depending on what branch of physics you are in ;-)

    Can be "Abscence of excitation" (i.e ground state), "Abscense of real particles" etc.

    If you like wikipedia, there is a quite nice section about physics vacuum.

    http://en.wikipedia.org/wiki/Vacuum#Quantum-mechanical_definition
     
  13. Dec 3, 2008 #12
    Which brings us back to the original question... what is it about the walls that make them "light-emitting"?
     
  14. Dec 3, 2008 #13

    malawi_glenn

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    but the vaccum in the vacuum chamber is "another" vacuum. With the term vacuum in vacuum chamber one means "absence of matter".

    I asked you to read the physics section: "Quantum-mechanical definition", so you could understand what a physiscists means when he is talking about THE vacuum
     
  15. Dec 3, 2008 #14
    I read it carefully, and it seems the whole point they were trying to make about the vacuum is that it is nowhere "empty", that is, devoid of energy content. Whether it is because of the very large scale (cosmic microwave background) or the very small scale (vacuum fluctuation), the physics vacuum is very much unvacuous, mainly because of all of these photons that are flying all over the place.

    I did not understand any kind of causal significance of the vacuum as regards the notion of photons. Rather, I understood only that photons are what make the vacuum everywhere non-empty.

    The original questioner asked about what causes photons, rather than the fact that they make something called a "vacuum" very much un-vacuumlike.
     
  16. Dec 3, 2008 #15

    malawi_glenn

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    Well you where referring to the vacuum chamber which was not mentioned in that section.

    You are again mixing concepts, you think that the physics vacuum I was refering to when I said "photons are cretaed from the vacuum" with the vacuum in the "vacuum chamber" which consists of photons from BB-radiation.

    So forget about EVERYTHING in that article, except that part of "Quantum-mechanical definition", and don't mix the concepts and different vaccua ;-)

    You have the same semantics problem when physicsists talks about "annihilation" of particles.... ;-)
     
  17. Dec 3, 2008 #16

    ZapperZ

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    In all of this, you seem to have not mentioned what are the "all kinds" of conservation law that is being broken. For example, in a Bremsstrahlung radiation, what conservation law is being broken there? In a synchrotron center where they generate light from hard x-ray to soft UV and IR by having the electron bunches passing through a series of undulators, what conservation laws are broken there?

    Zz.
     
  18. Dec 3, 2008 #17
    Is the fact that there may or may not be a conservation law that is ever broken in any conceivable situation relevant to the simple question of how photons are born? If the two concepts called "law of conservation of energy" and "the cause of photon creation" are related, then it what way are they related?
     
  19. Dec 3, 2008 #18

    ZapperZ

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    Photons are born because of the conservation laws - both spin and energy!

    But you are evading the question. You insisted that there were conservation laws broken. When you are asked directly to point out what these are, you are now trying to evade the question.

    So again, what ARE the conservation laws that are broken here?

    Zz.
     
  20. Dec 3, 2008 #19
    I made that statement before I realized that a physics vacuum has nothing whatever to do with emptiness. So I am taking back that reservation. A vacuum is just filled with stuff, that is always conserved, and that is also responsible for photon creation. But in what way it is responsible, I am still not sure.

    So now you say that conservation laws are the cause of photon creation. It seems to me that a conservation law just has to do with the "equilibrium" between photon destruction and photon creation.

    I don't see how the simple fact of the equality of the values shared between these two events goes very far in describing the physical nature of either of these events.

    So now the question is: are you going to evade that question?
     
  21. Dec 3, 2008 #20

    ZapperZ

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    What question? You asked me where photons come from. I answered.

    You will note that your claim that the light source I mentioned broke conservation laws were all that I was interested in. Since you took that back, I'm done. You should not confuse your discussion with malawi_glenn with what *I* was asking you on.

    Zz.
     
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